Marshal a General Dive

Estimate journey and dive timingsRoad journeys need to be based on experience, though computerised journey planners help a lot. Often not bad getting down there as typically early Sunday morning start. Allow more time in high summer though for weekender traffic. If meeting for breakfast somewhere, make sure there’s a clear departure time else time slips away very easily. Allow an hour once at site for preparing RIB, kitting up and launching. Sea trips are very variable. Depends on sea-miles, boat, tides and weather conditions. In practice, rare for our club to need more than half an hour to get to a site. If shotting a wreck, need to allow tons of extra time, even once on site: finding wreck may be hard, shotting it can take several attempts, and slack may be early. An hour is typically plenty even on the RIB (and if goes well can do it in ten mins flat). Normally need less with a good hardboat skipper.

Ensure right safety equipment aboardEnsure certain equipment available. If using hardboat and it doesn’t have Oxygen (always should but check), take club O2 kit. Check full well in advance. Ditto first aid. Club stuff normally kept with RIB anyway. Should be checked regularly. For RIB dives, take spare cylinder of air in case stage cylinder needed (or if bottle not full). Other kit standard: VHF radio, flares, fire extinguisher, anchor, spares… Diver recall signals a good idea too (underwater firecracker to tell divers to surface such as incident with other divers).

Arrange meeting points and timesMake sure everyone knows where/when to meet. Make clear that if not there on time, others may have left. Can’t afford to wait for people as delays cascade and ruin day for everyone else. Suggest car-shares or give names/numbers of others going on same trip. Ideally, swap mobile phone numbers in case of problems. If sites not known, try to provide map/directions. Make clear what the time refers to, no good people turning up at time stated if that’s the time boat needs to leave. Specify meet up time a good half hour before departure depending on how easy parking/loading is.

Make sure all dive details knownFor hardboat dives, ideal way is issue info sheet to all divers with everything they need to know on it. Things to make clear: meeting places/times; hints at travel times; types of dives; max depths; what equipment needed (2 cyls, SMB/DSMB, flags…); whether to take food/drinks; special considerations like poor shelter so take hat & coat etc.

Find out what the weather may doMore than a week out, hardly worth trying. Four or five days ahead, several sources. BBC early evening news around 7pm often gives long range idea of what weekend might do as early as Tuesday. Also, the website has free access weather outlook 4 days ahead see quick links at the top of the home page. Other than that there are the phone and fax services. Marinecall is a valuable aid, see: www.weathercall.co.uk/mc/ for details. It offers a range of services from recorded voice forecasts, SMS and WAP, fax, and a very handy Marine Weather Services Handbook (www.weathercall.co.uk/mc/mc_met_book.php) Marinecall voice service gives very useful details including forecast surf height and sea temperatures. Beware though, this is a premium rate service and will cost you a couple of pounds or more on your phone bill to get anything useful. Fax weather services also premium rate. Teletext on ITV has a page for coastal forecasts by region, and at one point in its cycle it shows tide times. On the day, listen to the shipping forecast on Radio 4. Gives details for all sea areas and most importantly note changes in wind direction and strength. If going to swing from off-shore to on-shore, and/or force increasing, beware that conditions will worsen and allow for it.

Decide if the weather is a problemMost important safety factors are sea swell and surface viz. High seas make people ill and often less disciplined. Greater risk of injury when thrown around on boat. Most importantly can be exceptionally hard to see surfacing divers. Launch and retrieve likely to be hazardous too. Beware diving in more than Force 4 with a typical RIB. However, swell also influenced strongly by wind direction and combination of wind and tide directions. If wind coming off the land, swell normally far less than if coming in off the sea. If diving in the lee of land too, lessens swell. If wind going in opposite direction to tidal flow, waves kick up higher and if wind flowing with tide, waves ease off. Can also get bigger waves if deep depressions in Atlantic sending swells in. Main thing to note is whether conditions likely to get better or worse? Will wind lesser or strengthen, will direction swing for better or worse? Will tide go more with wind, or more against it? Try to guess impact of all this then can use to judge whether safe to stay out longer or head for shelter early. Waves not the only problem. Fog highly dangerous as divers easy to lose and navigation harder. Cold weather very bad for poorly protected divers, and/or after cold water dives and/or long high speed runs back to shore as all increases risk of hypothermia. Sudden precipitation normally only a problem if causes problems with visibility or cold.

Decide whether to use SMBsDecide for yourself first (see “…Know when to use a Surface Marker Buoy”) but then if on hardboat, talk to skipper. May be special circumstances that change things. If any debate use SMBs anyway, and if any risk of tangling, at least use DSMBs. Check whether if skipper says “don’t need SMBs” that means truly no surface marker at all (rare) or DSMBs ok instead (far more common, and much safer). Don’t be lulled into carelessness by calm sea. Tracking bubbles is very hard even in good conditions, and sea can easily worsen during a dive making tracking impossible.

Buddy-pair the diversCan be hard to do well. Several factors to consider. Pairs must have right experience. Do any divers need looking after? Buddy them with experienced divers if so. After this, try to get pairs with similar air consumption. Also better to have pair using same suit: both semi or both dry rather than one of each. Try to arrange it so that at least one of each pair has redundant air supply if poss (twins or pony). Ideally have at least one of every pair with either computer or at least ascent rate warning (e.g. good watch or D-Timer) but make sure that if only one computer between two that both divers crystal clear how to dive defensively that way (see PDCs Crammer in download section for advice). Think about diving style: some divers swim like torpedoes, others bimble. Try to match. If anyone has a camera, pair them with a bimbler to avoid frustration. And don’t forget comfort factor. Ask if diver happy diving with your buddy suggestion and try to re-juggle if not. Getting best balance quite difficult sometimes. In practice often easiest to start with ‘obvious’ buddy pairs then see if can fit rest around this. If that no good, start swapping obvious pairs around. Odd numbers mean there will be a threesome. See “… Dive safely as a threesome” for advice and ensure divers fully briefed on how to do this safely. Finally – most important point: if can’t make safe pairings for everyone, no choice but to stand some divers down. Try make sure that another site available and all get two dives in the end to avoid mutiny, but ultimately safety over-rides all other considerations.

Keep everything moving quickly
So easy for time to trickle away and end up missing slack, only doing one dive or getting home really late. Make sure all know key timings. In particular if stopping for breakfast, make sure a departure time agreed stick to it. At launch site, marshall should make sure everyone doing something useful all the time. Needn’t be high-pressure/hassly, just watch for anyone ambling around looking useless or simply chatting and find them something to do. Good idea to ask questions rather than ‘command’, e.g. “is your kit ready for launch?” rather than “get your kit ready”. Delegate lots: e.g. get others to set up the RIB rather than fall into trap of thinking ‘quicker for me to do it as I know how’ – others will never learn this way.

Estimate the viz from the boatOnce in deeper water, look down into the sea where the water shaded from reflections (e.g. close against side of boat). In the UK, generally the blacker the better. If water looks green or milky, viz likely to be poor. In early summer can often see particles of plankton. Prolific fine plankton usually worse than sparse big globs of the stuff. Allow for sky conditions. Bright sunlight shows up particles more so dull conditions can make viz seem better than it is. Watch bubbles from props. Poor viz makes even bubbles near surface look green or brown. Good viz if can see even deep bubbles and they just look darker rather than green or brown tinted. This often gives useful guide to viz on dive, but beware that surface viz not a guaranteed guide to viz at depth. Crud can form layers in water at any depth, so good surface viz may yield to awful viz at, say, 15m; and even if poor viz at surface, can occasionally be good at bottom, though will be darker than normal for depth.

Brief the diversCheck echo sounder for max depth around dive site and tell divers. Describe site as far as poss. Describe major features (drawings ideal but rarely possible on UK boats), suggest good routes round them for best tour and forward dive profile (i.e. deep first, working shallower). Advise of any hazards: poor viz (see “… Estimate the viz from the boat”), unexpected drop-offs; wreck holds that may be entered accidentally, nasty current traps and so on. If diving at slack, state when slack window coming to an end and whether likely to be sudden or not (springs or neaps). Based on current dive depths, dive type, slack window and previous dives (if any), set maximum dive time by which diver to be back on surface. If any threesomes, remind of correct drill (see “… Dive safely as a threesome”). Decide if (D)SMBs needed (see “… Know when to use a Surface Marker Buoy”) and ensure divers have right kit. If doing drifts in little/no current, tell divers what compass bearing to follow (roughly) so all go in same direction. If doing wreck, describe whereabouts on wreck shot seems to be and what direction best to go in. Make sure divers and skipper all agreed whether divers can/should come back up shot line. If more than one boat on site, agree special pickup signal so skipper can tell his divers from others. Ensure divers know if boat might use Thunderflash diver recall signals and tell to surface immediately (within ascent rate & deco obligations) when they hear the bang. Also note recall signal that may be used if diving with SMBs – club standard normally four strong tugs on SMB line.

Watch for incidents in the makingLots of little signs can indicate potential trouble. Watch divers kitting up. Any divers slow or making mistakes – check if dived recently. If not buddy with experienced diver and limit max depth. Watch for anyone glossing over missing accessories (e.g. knife, watch, SMB…), or minor equipment failure. Look out for sea-sickness. Check sufferers carefully and insist on buddy check as these are ones who will miss things. Keep an eye on anyone looking flustered/rushed for same reason. Watch out for unaccustomed buddies who don’t talk to each other. Insist they talk through dive plan together.

Record important info before divesRarely done but important thing is to have emergency contact phone number for every diver. Imagine having a serious incident and not knowing who to tell… (skipper may insist on divers logging numbers anyway). DO can provide laminate list of club member contact numbers to take with you. DO or secretary has them on file too. Important too to note colour of divers’ kit. If divers swept away, rescue services need to know what to look for. Note colour of oods, suits, BCDs, cylinders, SMBs. Note if any divers have strobes, flares or EPIRBs & tech divers like Nitrox, trimix or rebreather. If marshalling from the surface, best to make a note of when each pair goes in (wax pencil on plastic best). If diving too (as often the case) ensure that skipper/cox will note times in. Tell divers when you expect them up and raise alarm as soon as cause for concern. Note specially if anyone diving on Nitrox or even Trimix and what is the mix.